1. Field of the Invention
The invention relates to an electrochemical storage cell of the alkali-metal and chalcogen type with at least one anode space for receiving the anolyte and a cathode space for receiving the catholyte, which are separated by an alkali ion-conducting solid electrolyte. The electrolyte is surrounded in the region of the anode space by a capillary structure at least over the entire surface utilized for the chemical reaction.
2. Description of the Prior Art
Such rechargeable electrochemical storage cells with a solid electrolyte are highly suited for constructing storage batteries with high energy and power density. The solid electrolytes used in the alkali/chalcogen storage cells, which are made, for instance, of .beta.-aluminum oxide are characterized by the feature that the partial conductivity of the mobile ion is very high and the partial conductivity of the electrons is many powers of ten lower. By using such solid electrolytes for constructing electrochemical storage cells, practically no self-discharge takes place, since the electron conductivity is negligible and their reaction substances, as neutral particles, also cannot get through the solid electrolyte.
A specific example for such rechargeable electrochemical storage cells are those of the sodium/sulfur type which have a solid electrolyte of .beta.-aluminum oxide. It is an advantage of these electrochemical storage cells that no secondary electrochemical reactions occur during the charging. The reason for this is again that only sodium ions can get through the solid electrolyte. The current yield of such a sodium/sulfur cell is therefore nearly 100%. In these electrochemical storage cells, the ratio of energy content to total weight of such a storage cell is very large as compared to lead storage cells, since the reaction materials are light and much energy is released in the electrochemical reaction. Electrochemical storage cells on the basis of sodium and sulfur therefore have considerable advantages over conventional storage batteries such as lead storage batteries.
To ensure optimum operation of these sodium/sulfur storage cells, there must be assurance that these storage cells have a low internal resistance. To achieve this in sodium/sulfur storage cells, it is necessary that the solid electrolyte is wetted or covered on both sides by one of the two reactants without a gap.
In German Pat. No. 24 00 202, an electrochemical storage cell is described which has a cup-shaped solid electrolyte, the interior of which serves as the anode space. An alloy steel fabric is placed in the interior of the solid electrolyte. Between the surface of the fabric and the solid electrolyte, a capillary region which extends up into the supply vessel of the alkali metal is created by this measure. The capillary structure formed thereby causes distribution of the alkali metal over the entire active surface of the solid electrolyte on the anode side.
A disadvantage of this arrangement is that the transport of the alkali metal from the supply vessel to the solid electrolyte surface and from there back to the supply vessel can take place only within the capillary structure. With increasing age of the storage cell, the danger exists here that the transporting action of the capillary structure is decreased by impurities. Thereby, the surface wetting of the solid electrolyte is reduced, which can cause a rise in the internal resistance of the storage cell and therefore, diminished operability thereof.